The present invention relates to apparatus and methods for processing substrates such as semiconductor substrates for use in IC fabrication or glass panels for use in flat panel display applications. More particularly, the present invention relates to improved processing systems that are capable of processing substrates with a high degree of processing uniformity across the substrate surface.
During the manufacture of a semiconductor-based product, for example, a flat panel display or an integrated circuit, multiple deposition and/or etching steps may be employed on the surface of a substrate to form devices such as transistors, capacitors, resistors, interconnects and the like. During deposition, successive layers of various materials are deposited on the surface of the substrate to form a layer stack. For example, layers of insulator, conductor and semiconductor may be formed on the surface of the substrate. Conversely, etching may be employed to selectively remove materials from predefined areas of the substrate, and more particularly the layer stack. For example, etched features such as vias, contacts, or trenches may be formed in the layers of the substrate.
Etching and depositing processes and their associated reactors have been around for some time. For example, deposition processes including chemical vapor deposition (CVD), thermal CVD, plasma enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD) such as sputtering and the like, as well as, etching processes including those adapted for dry etching, plasma etching, reactive ion etching (RIE), magnetically enhanced reactive ion etching (MERIE), electron cyclotron resonance (ECR), and the like, have been introduced and employed to various degrees to process semiconductor substrates and display panels.
In processing substrates, one of the most important parameters that engineers strive to improve is process uniformity. In the etch environment, for example, etch uniformity is an important determinant of uniform device performance and device yield, i.e., a high level of etch uniformity tends to improve the percentage of defect-free processed substrates, which translates into lower cost for the manufacturer. As the term is employed herein, etch uniformity refers to the uniformity of the entire etch process across the substrate surface including etch rate, microloading, mask selectivity, underlayer selectivity, critical dimension control, and profile characteristics like sidewall angle and roughness. If the etch is highly uniform, for example, it is expected that etch rates at different points on the substrate tend to be substantially equal. In this case, it is less likely that one area of the substrate will be unduly over-etched while other areas remain inadequately etched. Although not specifically described, it should be understood that deposition uniformity is similar to etch uniformity in that it is also an important determinant of uniform device performance and device yield.
In addition, in many applications these stringent processing requirements may be contradictory at different stages during the substrate processing. Often this is due to the presence of multiple layers that must be processed with dramatically different processing requirements. For example, etch recipes including power, temperature, pressure, gas chemistry, and gas flow may be required to dramatically change while processing a single substrate to achieve the desired processing performance. Furthermore, because of the nature of the processes, material may accumulate on surrounding surfaces, i.e., chamber walls, and as a result the process may drift.
In addition to processing uniformity, there also exist other issues of concern to the semiconductor industry. Among the important issues to manufacturers is the cost of ownership of the processing tool, which includes, for example, the cost of acquiring and maintaining the system, the frequency of chamber cleaning required to maintain an acceptable level of processing performance, the longevity of the system components, and the like. Thus a desirable process is often one that strikes the right balance between the different cost-of-ownership and process parameters in such a way that results in a higher quality process at a lower cost. Further, as the features on the substrate become smaller and the process becomes more demanding (e.g., smaller critical dimensions, higher aspect ratios, faster throughput, and the like), process engineers are constantly searching for new methods and apparatuses to achieve higher quality processing results at lower costs.
In view of the foregoing, there are desired improved techniques for producing uniform processing at the surface of the substrate.